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39
MARCH/APRIL 2018
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TVPJOURNAL.COM
FEATURES
Secondary Glaucoma
Secondary glaucoma ( FIGURE 2 ) results from a physical
obstruction to AH drainage, usually occurring at the
ICA or pupil. The ICA can become obstructed with
cellular debris (red blood cells, white blood cells,
tumor cells) or inflammatory proteinaceous debris.
The pupillary flow of AH may be obstructed by
iris adhesions to the lens (posterior synechia) or an
anteriorly luxated lens. Certain breeds, such as terriers,
Chinese crested dogs, and the shar-pei, are predisposed
to anterior lens luxation because of an inherited
abnormality in the lens zonule suspension system.
Acute glaucoma in these breeds should prompt the
clinician to look closely for an anterior lens luxation.
Duration of Glaucoma
Acute Glaucoma: This type of glaucoma ( FIGURE 3 )
is defined as an elevation in IOP of less than 12 to
24 hours' duration. If patients are treated during
this phase, vision may be salvageable. Unfortunately,
there are often subclinical spikes in IOP before the
sustained elevation, which are quite detrimental.
Thus, only about 50% of patients regain sight
even when treated in the acute phase.
1
Chronic Glaucoma: This type ( FIGURE 4 ) occurs
when the IOP elevation is sustained for days or
longer. Medical therapy may reduce the IOP, but
vision cannot be regained. With time, many of the
ocular structures undergo both physiologic and
FIGURE 1. Primary glaucoma. The right eye of an 8-year-old
female spayed basset hound with primary, chronic glaucoma.
Note the episcleral injection, corneal edema, buphthalmos,
and lens subluxation (secondary to buphthalmos). The retina
appears hyperreflective, with a significant lack of retinal
blood vessels (retinal degeneration).
FIGURE 2. Secondary glaucoma. The left eye of an 11-year-old
male castrated husky with secondary glaucoma. Note the
diffuse iris discoloration and focal region of hyphema.
TABLE 1 Key Aspects in Comparing Acute and Chronic Glaucoma
ASPECT ACUTE GLAUCOMA CHRONIC GLAUCOMA
Duration of IOP elevation <12–24 h Days to weeks
Globe size Normal Normal to buphthalmic
Menace response Usually absent* Absent
Direct PLR Usually absent* Absent
Indirect PLR Present Absent
Dazzle reflex Present Absent
Optic nerve/retina Normal to mildly pale optic nerve
Cupped, dark optic nerve, regions of
tapetal hyperreflectivity, generalized
vascular attenuation
*Depends on degree of IOP elevation and previous IOP spikes.